Phrag leaves yellowing as spikes begin to appear...

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It's a learning curve...
Aug 23, 2015
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Bourne, Lincolnshire, UK
Hi guys,

I think I've gotten a handle on the cause of this but would like to run it past the group just in case my research & thinking aren't 100%.

A little background; I've noticed over the past few couple of months that seemingly perfectly healthy and vigorous phrags started to yellow the leaves on their older (previously flowered) growths. The leaves would yellow quite quickly, eventually turning brown at which point I'd cut it off. At the same time, each plant that exhibited this would be sending up a spike or two from its new growth(s). Plants that haven't flowered because they're too young and one that just decided not to bloom yet have been either unaffected or much less so. The phrags are mostly hybrids with a couple of besseae clones from OZ and a besseae flavum I've had for a couple of years.

This isn't the usual very old leaf occasionally going yellow, it was several leaves at a time going very quickly, from the previous most recently flowered growth - I guessed because the plant was using the nutrients stored in the leaves because it wasn't getting the nutrients it needed from what I was giving it.

I water them every other day, they're planted in fir bark mix (with perlite and horticultural foam). Temps are daytime highs of 24-26 degrees with night time around 17-19 degrees. Humidity is around 60%-70% during the day and around 45%-55% at night.

I was feeding them on a pretty low fert dosage which in hindsight was probably far too low (1.8 | 1.2 | 2.1 at half strength every third watering)...

After speaking with a couple of people at a local orchid show recently, I was recommended to use something like Dyna-Gro 'Grow' which is 7 9 5 at full strength and at every watering would be fine for Phrags. I'd also read about occasional use of Epsom Salts so bought some of that from local garden centre.

Using just the Dyna-Gro, I watered with 1 teaspoon per gallon for a few waterings and then after I got the salts, I watered with a half dose of fert. together with 1 teaspoon per gallon of Epsom Salts for a couple of waterings, then flushed them through on the next. Now I'm giving them 5ml Dyna-Gro per 5 litres (which is approx. 1 teaspoon per gallon) at every watering with a view to another dose of Epsom Salts once per month with a flush through on the following watering.

Am I on the right track?

The plants have definitely 'greened up' and seem happier. I've been gradually taking the few phrags I still have in S/H, out as/when I repot them and I've not noticed any ill effects of them not being stood in trays of water anymore. Makes for easier watering/maintenance too :)

I use rainwater which around here has a TDS of about 24ppm with a PH of 6.5. When watering with just the Dyna-Gro, my TDS is about 400ppm and PH drops to 4.1.
I fertilize with a 16-16-16 sea grow 1 tsp per gal. twice a month alternating with peters excel cal mag 15-5-15 and flushing in between, it seems you need to up your dose of fertilizer, you also need to add calcium
Thanks for the advice. I've bought some Ionic CalMagPro to up the calcium and magnesium levels. I've given them a couple of doses of 1ml per litre at the last couple of waterings with a clean flush through on the third (most recent water).

Would I now switch to the recommended does of 2.5ml per 5 litre and water this at every other watering or?
As well as going down the little and often route with phrags and akerne's rain mix I saw another improvement when I started to use some alkaline growstones in the potting mix or just added to the water that the phrags stand in.
Not sure what they added but they greened up the plants from paleish to dark green very quickly.
Maybe they added extra calcium or magnesium like you are suggesting to do,